This invention relates to a circuit arrangement used in conjunction with devices which determine a distortion characteristics of a data transmission link for causing the phase of a received data element pulse train forming a reference signal to follow a signal transmitted through a transmission link, the received element pulse train being obtained using a timing signal produced by a pulse generator and a frequency-divider. In this context, by means of a synchronizing device a delay or lead is produced in individual pulses of the timing signal with lagging or leading distortion. The synchronizing device contains a counter which, on receiving counting pulses and depending upon the binary values of the received element train, increases or reduces its count, producing a signal when the count reaches zero.
In one known system for testing a transmission link, a test signal is transmitted through the link, and at the receiving end, the distortion of the transmitted signal is measured using a distortion meter, the received element train generated at the receiving end being used as the reference signal. Also, at the receiving end an error counter can be provided which is supplied with the transmitted test signal and with an identical test signal generated at the receiving end. However, this counter counts the number of errors occurring in the transmitted signal. In so doing, by means of a synchronizing device, the received element train is made to coincide in terms of frequency and phase with the transmitted signal.
An object of this invention is to provide a synchronizing device by means of which, in adjusting the frequency and phase of the reference signal, the accuracy of measurement of the error counter and/or of the distortion meter is affected as little as possible.
It is another object of this invention is to provide a synchronizing device which is designed to operate along a rectangular control characteristic, and is designed so that the instants of scanning, even in the presence of one sided distortion, occur at the centers of the elements in the transmitted signal.